Compressor Installation With a Water-Injected Compressor Element

ABSTRACT

Compressor installation with a water-injected compressor element to which an inlet line ( 4 ) and an outlet line ( 5 ) are connected, an air inlet filter ( 13 ) to which said inlet line ( 4 ) is connected, a water separator ( 6 ) into which said outlet line ( 5 ) feeds and a return line ( 7 ) between this water separator ( 6 ) and the compressor element ( 2 ), characterised in that said air inlet filter ( 13 ) takes the form of a wet filter to which a water supply is connected.

This invention relates to a compressor installation with awater-injected compressor element.

More specifically, the invention relates to a compressor installationwith a water-injected compressor element to which an inlet line and anoutlet line are connected, an air inlet filter to which said inlet lineis connected, a water separator into which said outlet line feeds and areturn line between this water separator and the compressor element.

In water-injected compressor elements, the rotating parts, and inparticular the screws in screw compressor elements, are lubricated withwater instead of with oil. This water also serves as a sealant betweenthese rotating parts and ensures cooling, making virtually isothermiccompression possible.

The humidity of a gas, and of air in particular, is a function of itstemperature and pressure. Within the compressor element, the gas ismixed with water and the gas at the outlet from the compressor elementis thus always 100% saturated.

Depending on the absolute humidity of the intake gas and the pressure atthe outlet from the compressor element, a water-injected compressorelement will thus either consume or produce water. The higher theabsolute humidity of the intake gas and the higher the outlet pressure,the smaller the amount of water that will be consumed. On the otherhand, the compressor element will consume more water if the absolutehumidity at the inlet falls and/or the pressure in the outlet is lower.

This is why known compressor installations with a water-injectedcompressor element also have a water supply device to add water ifnecessary.

It is customary to inject the water that needs to be added via thereturn line, directly between the rotating elements or at the compressorelement's inlet.

However, this water must meet strict requirements.

The water that is consumed, is chemically pure water, so that waterconsumption will cause the concentration of salts and other suchsubstances in the remaining water to rise if ordinary water is added.This can cause damage to the compressor element, and in particular theseals and bearings.

The addition of extra water or the consumption of pure water could alsochange the pH value of the water in the circuit, which can again in turncontribute to corrosion.

For these reasons, it is known to add the water via reverse osmosis,which makes the water supply device relatively expensive.

According to WO-A-96/21109, the water that has been separated out in thewater separator after the compressor element, is returned to thiscompressor element through an ioniser in which natural minerals insolution in the water, such as silicon, calcium, magnesium and iron, areconverted into hydroxide form, after which they acquire an electricalcharge.

Because the hydroxide particles have the same polarity, they areprevented from clumping together and hence from precipitating. However,as these particles only retain their charge temporarily, the ionisationhas to be continually repeated, and the recycled water has to be pumpedthrough the ioniser several times a minute. Moreover, precipitation isnot completely excluded, and this injected water also has to be filteredto prevent other impurities.

The aim of the present invention is to offer an answer to one or more ofsaid and certain other disadvantages.

To this end, the present invention relates to a compressor installationwith a water-injected compressor element to which an inlet line and anoutlet line are connected, an air inlet filter to which said inlet lineis connected, a water separator into which said outlet line feeds and areturn line between this water separator and the compressor element,with said air inlet filter taking the form of a wet filter to which awater supply is connected.

Through the injection of water into the air inlet filter, this air issimultaneously humidified and purified, as impurities are captured bythe injected water droplets and conducted away. A portion of theinjected water will evaporate and be conveyed in the air flow to thecompressor element.

Because a portion of this water which has been injected into the airinlet filter enters the compressor element along with the intake gas inthe form of water vapour, this water is chemically pure, and neither thelevel of minerals and salts nor the pH of the water for water injectionis affected.

A compressor installation of this type has the advantage that thecompressor element's inlet air can be humidified to such a degree thatduring periods when the environmental air is dry, no extra supply ofdemineralised water or water that has been purified by means of areverse osmosis unit is needed any longer.

Another advantage of such a compressor installation according to theinvention is that it can be produced relatively cheaply, and that itdisplays a considerably higher filter efficiency than traditional airfilters without water injection.

A further advantage is that the air inlet filter of such a compressorinstallation according to the invention causes a smaller fall inpressure than traditional dry air filters, thus increasing thecompressor efficiency.

Yet a further advantage of such a compressor installation is that itenables water to be added relatively simply and inexpensively withoutreducing the quality of the water present in the circuit and without anyrisk of damaging the compressor element by increasing the deposition ofminerals and similar substances.

An additional advantage is that in speed-regulated compressors, no inletvalve or so-called “unloader” is needed any longer between the air inletfilter and the inlet to the compressor element to absorb any waterhammer which occurs when the compressor is stopped, as the water hammercan escape via the inlet line, which is introduced between the air inletfilter and the compressor element, where applicable to a water drainageline from this wet air inlet filter.

Preferably, said air inlet filter will take the form of a housing inwhich a substrate is introduced through which the intake air is passed;this substrate should preferably take the form of a material with anopen cellular structure, such as polyurethane foam, polyethylene or asimilar material.

As a result of the air inlet filter having this structure, the contactsurface between the water and the intake air is increased, which meansthat the air is optimally humidified and purified.

Another preferred characteristic of a compressor installation accordingto the invention is that said air inlet filter is provided with anelement for stopping water drops in the gas flow, in order to preventwater drops being brought in with the intake air.

In the preferred embodiment of a compressor installation according tothe present invention, said water supply is constituted by a lineconnecting to said water separator.

This has the advantage that the water derived from this water separatorcan be used by being injected into this air inlet filter, therebyenabling the supply of extra water to be restricted.

A further advantage is that the air inlet filter in such a compressorinstallation operates on a self-cleaning basis due to being periodicallysprayed with pure water derived from the water separator.

In a further preferred characteristic of the invention, said watersupply to the air inlet filter takes the form of a supply device forextra water.

This embodiment has the same advantages as an embodiment in which theadded water is derived from the water separator, and also makes itpossible to add extra water to the compressor installation.

With a view to demonstrating the invention's characteristics moreclearly, in what follows, by way of example and without any limitativeintention, a preferred embodiment of a compressor installation accordingto the invention with a water-injected compressor element is described,with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of a compressor installationaccording to the invention;

FIGS. 2 and 3 illustrate the working of a compressor installationaccording to FIG. 1;

FIGS. 4 and 5 show regulating curves which are followed during theworking of a compressor installation according to FIG. 1, the first in anormal situation with sufficient water vapour in the intake air and thesecond for a situation with very little water vapour in the intake air,for example during extreme winter weather.

FIG. 1 shows a compressor installation 1 according to the inventionwhich is provided with a compressor element 2, for example in the formof a screw compressor element, which is driven by a motor 3 and to whichan inlet line 4 is connected. To the outlet from the compressor element2 is connected an outlet line 5 which feeds into a water separator 6.

A return line 7 connects the underside of the water separator 6 with thecompressor element 2. In this return line 7, a cooling device 8 is setup which in this instance, though not necessarily, is cooled by means ofa fan 9 which is driven by a motor 10.

However, said cooling device 8 can also take many other forms, such asthat of a liquid-liquid heat exchanger.

On top of the water separator 6 is fitted a minimum pressure valve 11 ofthe known type for compressed air; this opens at a pre-set openingpressure in the water separator and a compressed air line 12 isconnected to it for the supply of compressed gas to a mains network.

Into said inlet line 4 an air inlet filter 13 is introduced which inthis case consists of a housing 14 with an air inlet 15 and an airoutlet 16 to which said inlet line 4 is connected. In this housing 14, asubstrate 17 is introduced through which the intake air is passed.

Said air inlet filter 13 should preferably also be provided with anelement 18 or “demister” to prevent water drops in the gas flow, and awater drainage line 19 for contaminated water.

Said substrate 17 and the element 18 should preferably both take theform of a material with an open cellular structure, such as polyurethanefoam, polyethylene or a similar material. Obviously, the invention isnot restricted to the use of any one of these materials for theproduction of the substrate 17 and the element 18, and numerous othermaterials may also be used.

In a preferred embodiment of a compressor installation 1 according tothe invention, the substrate 17 and/or the element 18 consists of amaterial that is doped with one or more bacteriostatic agents, such asnano-silver. It is clear, however, that this is not a requirementaccording to the invention.

In the present instance, said substrate 17 is located at the bottom ofthe housing 14, while the element 18 is introduced at the top of thishousing 14. Said air inlet 15 is provided at the bottom of the housing14, opposite the substrate 17, while the air outlet 16 is fitted at thetop of the housing 14 of the air inlet filter 13, opposite the element18.

Said air inlet filter 13 takes the form according to the invention of awet filter to which a water supply is connected which, in this instance,takes the form of a line 20, one end of which is connected to said waterseparator 6 and the other end of which is connected to said air inletfilter 13 and connected to a sprinkler 21 which issues into this airinlet filter 13, and more particularly between the substrate 17 and theelement 18.

In said line 20 between the water separator 6 and the air inlet filter13, a controlled valve 22 is introduced.

The compressor installation 1 is also provided with a supply device 23for extra water which in this instance also forms part of said watersupply to the air inlet filter 13 and which, in this instance, isconnected via a sprinkler 24 to said air inlet filter 13.

Said supply device 23 consists principally of a supply line 25, forinstance for tap water, into which a controlled valve 26 and a waterfilter 27 are introduced.

Said water filter 27 preferably consists of an absolute water filterwith a filter rating of 5 micrometres, and whose so-called β value is1000, in other words whose efficiency is 99.9%. However, if desired, usecan also be made according to the invention of a nominal water filter,although the latter's efficiency is usually lower than that of anabsolute water filter.

The term β value refers here, as known, to the ratio between the numberof particles of a given size which are present in the water flow beforefiltration to the number of particles of the same size which are presentin the water flow after filtration.

In this instance, though not necessarily, said supply device 23 forextra water is additionally provided with a water conditioner whichensures that no calcification occurs in the sprinkler 24. This waterconditioner consists in this instance of two powerful permanent magnets29 and 30 which are set up at an angle of 90° with their south polespointing towards the spray nozzle of the sprinkler 24.

At least said sprinkler 24 is preferably made of non-ferrous metal (suchas brass or CuNi), so that the water in the nozzle is always in themagnetic field and calcification can never occur in this sprinkler 24.Preferably, one or both sprinklers 21 and/or 24 will take the form of aso-called “flat jet sprinkler” which has a slot-shaped opening ratherthan a hole in order to prevent any deposits.

Preferably, said sprinklers 21 and 24 both feed into the housing 14 ofthe air inlet filter 13, and more specifically between the substrate 17and the element 18, and are both made of stainless non-ferrous metal. Itis also preferable for both of these sprinklers 21 and 24 to have aninternal filter to prevent the very fine nozzle from becoming blocked.

In a preferred embodiment said sprinklers 21 and 24 are of the type thatdischarges 0.9 litres of water per hour at a pressure of 7 bar (7000hPa). Obviously, however, the sprinklers 21 and 24 are not restricted inthis respect, and numerous other types can be used.

The compressor installation 1 according to the invention is also fittedin this instance with a level regulator which is not shown in thefigure; this is connected firstly with a minimum and maximum levelsensor, respectively at levels A and B, in the water separator 6, andsecondly with said controlled valves 22 and 26.

The working of a compressor installation according to the invention isvery simple and is shown in FIGS. 2 and 3.

When the compressor element 2 is driven by the motor 3, air is drawn inthrough the air inlet filter 13 and via the inlet line 4; it is thencompressed by the compressor element 2 and conveyed via the outlet line5 to the water separator 6; it is then sent via the minimum pressurevalve 11 into the compressed air line 12.

The water that is separated out from the compressed air by means of saidwater separator 6, is sent via the return line 7 through the coolingdevice 8 and is then injected into the compressor element 2 to lubricateand cool the rotating parts of the compressor element 2.

In the situation shown in FIG. 2, the water level in the water separator6 is at a given maximum level A. This is detected by said maximum levelsensor and signalled to the level regulator, which reacts by opening thevalve 22, with the result that, under the influence of the pressurebuild-up in the water separator 6, water is forced via the line 20 tothe sprinkler 21 and injected into the air inlet filter 13.

Water drops which splash downwards humidify the cellular substrate 17and fall through this substrate 17 to the water drainage line 19, as aresult of which the substrate 17 becomes completely wet. Water dropswhich splash upwards, are stopped by the element 18 which also has acellular structure, with the result that only the underside of thiselement 18 is humidified and water drops are prevented from findingtheir way into the inlet line 4.

The intake air which enters the air inlet filter 13 via the air inlet15, counterflows against the falling drops in the substrate 17, as aresult of which the air is purified and humidified by the water drops.

The vast majority of these drops will, together with dust particleswhich have been collected in the substrate 17, be conveyed away via thewater drainage line 19, while a portion of these drops evaporates andenters the air flow.

The filtered and humidified air flows through the element 18 to the airoutlet 16 of the air inlet filter 13 and is then drawn along the inletline 4 by the compressor element 2, where, together with the injectedwater, it is compressed, and the mix of compressed air and water isconveyed via the outlet from the compressor element 2 to the waterseparator 6.

Via said minimum pressure valve 11 on the water separator 6, thecompressed gas is finally conveyed to the compressed air line 12-,possibly via a freeze-dryer or cyclone water separator not shown in thefigures to which the compressed air outlet on the water separator 6 isconnected.

If use is made of such a freeze-dryer or cyclone water separator, areturn line may be fitted if required, for example to the inlet on thecompressor element 2.

If more water vapour is drained away with the compressed air via thecompressed air line 12 than enters with the intake air via the inletline 4, which thus means that water is being consumed, the water levelin the water separator 6 will fall.

For example, this is the case in winter, when the absolute humidity ofthe environmental air is less than or equal to 2 g/kg.

In this instance, as shown in FIG. 3, as soon as a given minimum waterlevel B is reached in the water separator 6, the supply device 23 forextra water is activated by the level regulator opening the valve 26,while the valve 22 in the line 20 between the water separator 6 and theair inlet filter 13 is closed.

The extra water that is brought in via the supply line 25 is first ofall passed through the water filter 27, as a result of which anycontamination which may be present in this extra water can be filteredout.

However, there may also be minerals contained in the supplied water,such as calcium ions. Such ions can flow through the water filter 27 andbecome deposited in the sprinkler 24, causing it to become blocked up.

To provide a solution to this, use can be made for example of a waterconditioner, which ensures that no calcification occurs, and which ispreferably of the type described above, which generates a magnetic fieldwhich affects the calcium ions in such a way that they are unable toadhere for a certain length of time, with the result that the sprinkler24 is protected against calcium deposits.

The extra water is then injected through the sprinkler 24 into the airinlet filter 13, where the substrate 17 is humidified in a manneranalogous to that described earlier and the air is purified andhumidified by the water drops.

Any contamination and minerals still present in the injected watercannot evaporate but adhere to the substrate 17 or to the underside ofthe element 18. A portion of the contamination particles is dissolved bythe water drops and conveyed away to the water drainage line 19.

The element 18 stops the drops in a manner analogous to that describedearlier, so that the outgoing air in the inlet line 4 is free of waterdroplets and only consists of air and water vapour.

Through the supply of extra water via the valve 26, as shown in FIG. 4,the water level L in the water separator 6 will rise until the maximumwater level A is reached, whereupon the valve 26 in the supply device 23is closed again and the valve 22 is opened again.

By controlling the valves 22 and 26 it is mostly the case that, whenthere is more water vapour present in the intake air than in thedelivered compressed air, the rise in the water level L in the waterseparator 6 will occur faster than its fall, as shown diagrammaticallyby the top curve in FIG. 4.

While extra water is being supplied via the supply device 23 via supplyline 25, there is no continuous loss of water from the water separator6. As a result, the water level L in the water separator 6 will rise.

As a result of the extra humidification of the intake inlet air by theair inlet filter 13, the maximum water level A will quickly be reached.As the time during which extra water is conveyed into the air inletfilter 13 is limited, the consumption of water, for example from themains network, is also limited.

Once the maximum water level A in the water separator 6 has beenreached, the valve 26 on the supply device 23 will be closed and thevalve 22 on the line 20 will be opened.

The period during which the valve 22 is open, will in this instance beconsiderably longer than the period during which it is closed, as isshown in the centre-most curve D in FIG. 4, and conversely, as shown inthe bottom curve E in FIG. 4, the open position of the valve 26 will bemaintained for a shorter period than its closed position. The open andclosed positions of the valves 22 and 26 are denoted by O (open), and C(closed), respectively.

By contrast, if the absolute humidity of the inlet air is lower than theabsolute humidity of the delivered compressed air, as is usually thecase in extreme winter conditions, there will be more consumption ofsupplied water via the supply device 23.

As a result, as shown in the centre-most curve F in FIG. 5, the periodduring which the valve 22 is open will be shorter because, in additionto the continuous leakage of water from the water separator 6 to thesprinkler 21, the continuous water consumption due to the low absolutehumidity of the inlet air will also ensure that the minimum water levelB in the water separator 6 is reached more quickly, as is illustrated bymeans of the top curve in FIG. 5.

By contrast, the period during which the valve 26 is open will, as shownin the bottom curve G in FIG. 5, be longer because the continuousconsumption of water from the water separator 6 due to the extremely lowabsolute humidity of the inlet air has to be compensated for. Duringthese periods, the extra water consumption will be higher than duringnon-winter periods.

This will mainly occur in countries which experience periods of freezingweather in the winter. The closer to the equator, the less frequent thissituation will occur, since the absolute humidity of the air increasesas one approaches the equator.

A compressor installation 1 according to the present invention is notrestricted to an embodiment as shown in the figures in which said watersupply to the air inlet filter 13 is provided by both the line 20 andthe supply device 23: according to the invention it is also possible forthe water supply to this air inlet filter 13 to consist of just one ofthese mechanisms.

According to the invention, the possibility is also not excluded of anadditional level sensor being fitted in the water separator 6, at alevel below the minimum water level B and connected with a controlmechanism which controls said motor 3. In this way, where there isextremely high water consumption and the water supply is insufficient tocompensate for the consumption or in the event of a fault in the minimumlevel sensor, the compressor element 2 can be switched off.

In all the embodiments, problems of deposition of minerals and salts inthe screw compressor element 1 are avoided in a simple and inexpensiveway and better volumetric efficiency is obtained. The water quality inthe circuit remains constant and is thus not altered by the extra supplyof water when water is being consumed.

The quality of the extra supplied water is of no importance, as onlywater vapour and hence chemically pure water ends up in the screwcompressor element 1. This can be very important when the compressorinstallation is located in places where no pure water is available.

By a special characteristic of the invention, the compressorinstallation is not provided with an inlet valve or so-called “unloader”to absorb any water hammer which occurs when the compressor is stopped.

The invention is by no means limited to the embodiments described andshown in the figures in the foregoing: such a compressor installationwith a water-injected compressor element may be produced in a number ofdifferent variants without going beyond the scope of the invention.

1-22. (canceled)
 23. Compressor installation comprising a water-injectedcompressor element to which an inlet line and an outlet line areconnected, an air inlet filter to which said inlet line is connected, awater separator into which said outlet line feeds and a return linebetween the water separator and the compressor element; said air inletfilter comprising a housing with an air inlet and an air outlet to whichsaid inlet line is connected, and a substrate in the housing throughwhich the intake air is passed; wherein said air inlet filter comprisesa wet filter to which a water supply is connected; said substratecomprising a material with an open cellular structure; and said watersupply comprising at least one of: a line which is connected to saidwater separator and a supply device for extra water.
 24. Compressorinstallation according to claim 23, wherein said substrate is made ofpolyurethane foam or polyethylene.
 25. Compressor installation accordingto claim 23, wherein said substrate comprises a material that is dopedwith one or more bacteriostatic agents.
 26. Compressor installationaccording to claim 25, wherein said one or more bacteriostatic agentscomprises nano-silver.
 27. Compressor installation according to claim23, wherein said air inlet filter is provided with an element forstopping water drops in the gas flow, to thereby prevent water dropsfrom being brought in with the intake air.
 28. Compressor installationaccording to claim 27, wherein said element comprises a material with anopen cellular structure.
 29. Compressor installation according to claim27, wherein said element comprises polyurethane foam or polyethylene.30. Compressor installation according to claim 27, wherein said elementcomprises a material that is doped with one or more bacteriostaticagents.
 31. Compressor installation according to claim 30, wherein saidone or more bacteriostatic agents comprises nano-silver.
 32. Compressorinstallation according to claim 23, wherein said air inlet filter isprovided with a water drainage line for contaminated water. 33.Compressor installation according to claim 23, wherein said water supplycomprises a line which is connected to said water separator. 34.Compressor installation according to claim 33, wherein, in said linebetween the water separator and the air inlet filter, a controlled valveis provided.
 35. Compressor installation according to claim 23, whereinsaid water supply comprises a supply device for extra water. 36.Compressor installation according to claim 35, wherein said supplydevice for extra water is provided with a controlled valve and a waterfilter.
 37. Compressor installation according to claim 36, wherein saidwater filter of the supply device for extra water comprises an absolutewater filter.
 38. Compressor installation according to claim 36, whereinsaid supply device for extra water is additionally provided with a waterconditioner arranged to prevent calcification.
 39. Compressorinstallation according to claim 38, wherein said water conditioner isprovided with two permanent magnets.
 40. Compressor installationaccording to claim 39, wherein said permanent magnets are arranged at anangle of 90° with their south poles pointing towards the spray nozzle ofa sprinkler with which said supply device for extra water is connectedto said air inlet filter.
 41. Compressor installation according to claim40, wherein said sprinkler is made of non-ferrous metal.
 42. Compressorinstallation according to claim 40, wherein said sprinkler comprises aflat jet sprinkler with a slot-shaped opening.
 43. Compressorinstallation according to claim 34, including a level regulator which isconnected firstly with a minimum and maximum level sensor in the waterseparator, and secondly with said controlled valves.
 44. Compressorinstallation according to claim 23, without an inlet valve arranged toabsorb water hammer when the compressor is stopped.